Certain amine-functional silicones have been used as components of hydrophilic treatments for softening fibrous substrates such as textiles, hair, and tissue. In addition to the silicone block, suitable molecules for such hydrophilic treatments may include, for example, amine groups to facilitate adsorption onto the substrate surface.
Many problems commonly are associated with amine-functional silicones used for treating textiles, particularly, the combination of yellowing and the tendency of the treated materials becoming increasingly hydrophobic over time. The chemical nature of the amine functionality to oxidize results in the yellowing. The reorganization or redistribution of the generally hydrophobic silicone chains results in the loss of hydrophilicity of the treated substrates. Thus, ongoing efforts have involved modifying amine-functional silicones by adding hydrophilic groups to siloxanes and by altering or reducing amine content to reduce yellowing.
Amine functionality in silicone polymers can be imparted in terminal positions (at the end of the polymer chain), in pendent positions (from functional groups attached to silicon atoms in the middle of the polymer chain), or both. A polymer with only terminal amine groups represents the absolute minimum amount of amine that may be present while guaranteeing that each and every polymer chain has the essential ability to attach to the surface of the substrate. The terminal amine also serves as a functionality from where larger or diverse telechelic polymers may be synthesized. One potential drawback is dependence of the amine content of the polymer relative to the molecular weight of the overall polymer. Pendent amine groups allow for the overall amine content of the polymer to be tuned. However, statistics dictate the distribution of the amine functionality among the chains and can be problematic in cases where low amine content is targeted and can result in some polymer chains lacking the functionality. A combination of both terminal and pendent amine groups would allow for the inclusion of amine functionality on each and every polymer chain while also allowing the overall amine content to be tuned for the polymers. No methods currently exist for synthesizing silicone-polyether block copolymers that include both terminal-amine groups and pendent-amine groups at a consistently reproducible level.
For example, in the approach disclosed in JP09183854 and JP03269570, a copolymer is prepared by first making a block copolymer from Si—H-terminal polydimethylsiloxane and a methallyl-terminal polyether. The resulting copolymer is equilibrated with a variety of functional siloxanes, such as an aminosiloxane, to make a silicone-polyether block copolymer having pendent functional groups, such as amine groups. In this sense, “equilibration” involves allowing the reaction to progress until the distribution of pendent functional groups within the copolymer is sufficiently random. No amine-functional endblocking agent is present in the reaction mixture; hence, the copolymers do not comprise terminal amine groups.
Several problems arise with respect to the scheme in JP09183854 and JP03269570. In the first step, for example, molecular-weight control is accomplished only by precisely controlling the ratio of olefin to Si—H. The success of the hydrosilylation reaction is sometimes dependent on a significant amount of solvent being added to make the silicone compatible with the polyether to enable efficient reaction. In some cases, significant amounts of Pt catalyst are added to drive the reaction to occur at an appreciable rate. In the second step, a long reaction time may be necessary to ensure complete randomization of the amine groups. Moreover, complete randomization of the amine groups can be difficult to discern from the reaction mixture. And because the amine groups are pendent, the resulting polymers exhibit a statistical distribution of amine groups across all the polymer chains that are formed. Thus, when the reaction mixture has a low amine concentration, a significant portion of the polymer chains would be expected to contain no amine functionality.
In WO 2008/127519, an epoxy-terminal silicone-polyether copolymer is synthesized by a slightly different route. Particularly, a Si—H-terminal polydimethylsiloxane is reacted with a polyether possessing hydrosilylatable endgroups (typically allyl or methallyl) polyether and an allyl-functional epoxide. The epoxy, which commonly is allyl glycidyl ether but may also be vinylcyclohexene oxide, provides a reactive site for the addition of a primary or secondary amine. This reaction can be conducted without a solvent under some conditions, depending primarily on the molecular weights of the polydimethylsiloxane and polyether. In the simplest form, this approach permits amine incorporation, but onto the chain ends only. But advantageously, nearly all the copolymer chains contain terminal-amine functionality, and the number of non-amine-functional chains is minimized. If one was to use a primary amine or secondary diamine in the reaction with the epoxy-terminal silicone-polyether copolymer, a chain-extended variant could be obtained also possessing tertiary amine groups along the chain.
Despite its advantages, the approach in WO 2008/127519 also has many undesirable attributes. First, precise control of the ratio of the Si—H-functional polymer and the unsaturated polyether are required to maintain control of the molecular weight of the initial intermediate. Second, because the approach requires a minimum of three processing steps, manufacturing costs can be high relative to the markets the eventual product could serve. Third, the use of solvent, which is often required, reduces process throughput and efficiency. Fourth, reagents such as allyl glycidyl ether and vinyl cyclohexene oxide can raise health or environmental concerns, particularly in light of regulations that limit the free-epoxide content in the final commercial product. Isomerization or hydrogenation of the epoxide double bond can lead to residual epoxides in excess of the regulated amount. Fifth, when substantial excesses of amine are required to drive the amination of the epoxide, unreacted amine must be removed in additional processing steps. Residual volatile amines typically cause undesirable odors in products, and low molecular-weight amines can be hazardous to aquatic life. Sixth, because each polymer chain contains the amine at only the two endgroups or junctions of the original epoxy-terminal silicone-polyether copolymer, the molar-fractional amine content of the copolymer decreases as molecular weight increases.
Therefore, there remains a need for silicone-polyether block copolymers that are functionalized with terminal-amine groups and, optionally, with one or more pendent-amine groups. There remains a further need for reliable and reproducible synthetic methods that avoid the above disadvantages of existing methods for incorporating limited amine functionality into silicone-polyether block copolymers.